Trunking system



. June 10,1930. V F. s. ENTZ 1,763,036

I I TRUNKING SYSTEM Filed Aug. 51, 1928 6 Sheets-Sheet 1 1764 &

INVENTUR' FERDINAND 5'. EN??? A mRA/ June 10, 1930.

fie. Z.

F; s. ENTZ TRUNKING SYSTEM Filed Aug. 51, 1928 INVENWR 6 Sheets-Sheet, 2

FERDINAND .5. EM:

A T TOR/YE Y June 10, 1-930. 7 v F. s. ENTZ 1,763,035

I TRUNKING SYSTEM Filed Aug. 31, 1928 6 Sheets-Sheet 3 A RNEY 'June 10, 1930. v

F. s. ENTZ TRUNKING SYSTEM Filed Aug. 51, 1928 FERDINAND 5T ENTz BY I 6 Sheets-Sheet 4 A T Y June 10, 1930. F. $.ENTZ 5 TRUNKING SYSTEM Filed Aug. 51, 1928 GSheets-Sheet 5 //v VENTDR FERDINAND 5'. EN TZ A TTURNEK June 10, 1 930 .F. s. ENTZ TRUNKING SYSTEM Filed Aug. 5-1, 1928 6 Sheets-Sheet I 6 w it MSKLS Patented June 10, 1930 I UNITED STATES A-TEN-r iaoerica" FERDINAND s. ENE, 01; MOUNT vERNoN, NEW YORK, Ass'reiioR'ro'RELL mnLErHoNn I LABORATORIES, INCORPORATED, OFNEW YORK, Y., A co Po ArIoN'oF ew YORK TRUNKING sYs'rRM Application filed August.31,'1928.' s mi No. 303,161.

- The present invention relates to a trunking system in which a telephone connection 1s built up by the interconnection of trunks at various telephone ofl'ices. More specifically, it relates to a trunking system'wherein repeaters may be'automatically added at certain ofiices as the telephone connection is built 7 he object of this invention is to provide an improved system of tandem straightfor' ward long distance trunking. V

One embodiment of the present invention comprises an arrangement'in the trunks of the tandem trunk telephone office for auto matically determining the character of trunks extended to another office in order that a repeater may 'be inserted in series wlth the trunk conductors if the trunk is of a character to require it. The operator at the tandem office is given the destination of the trunk connection by another operator and connect-s the terminating end of the tandem trunk to an outgoing trunk extending to the desired oifice. Responsive to this connection, the character of the outgoing trunk is determined by discriminating apparatus in the tandem lecting arrangement with automatic listening circuits at the tandem offices and atthe com- 7 pleting trunk ofl'ices to which the trunks are ordinarily extended from the tandem ofiice. Responsive to the selection of a trunk to a tandem office by a subscribers switchboard operator, the operators telephone set at a tandem switchboard is automatically associated'with the selected trunk. Threeshort impulses of tone are transmitted as a signal to the subscribers operator that a tandem operators telephone set is connected to the trunk. The name of the required completing olfice is then transmitted to the tandem operator who selects an outgoing trunk extending to that office orto a second tandem oifice. Assuming that arepeater is required for the outgoing trunk a selection is made and the repeater connected in series with the trunk conductors. This trunk may at times be extended to a second tandem oflice in which case the telephone set at the second tandem oflice is automatically connected to the-trunk in response to the selection of the repeater at the precedingtandem'oflice'. Three'short impulses of tone are again transmitted to the l v subscribers operator and the name of the required completing 'office is repeated by the subscribers operator. If a repeater is required for the trunk extending from the second tandemofiice, it is selected upon the operation of the discriminating apparatus. In

any event, theinsertion of the repeaterin the trunk at a'tandem ofice causes a telephone set atthe succeeding office to be'as'sociated-with the trunk conductors. When the succeeding office is a tandem completing trunkofiice two short impulses of 'tone are transmitted from the completing trunk position to the subscrib- I ers operator as'a signalthat the operator is prepared to receive the wanted subscribers station designation. ='T-his designation is board'circuit and apparatus is shown which telephone set tothe selected trunk; n

Fig; 2 illustrates'the tandem position apparatus and circuits including means for determining the character of outgoing trunks and initiating the selectionof a repeater. Fig. 3 illustrates a tandem completing automatically connects the tandem operators trunk circuit and a line circuit associated with a subscribers station.

Fig. 4 shows finding the trunk circuit over which the connection has been established and for selecting an idle repeater. Control relays are also shown in this figure.

Fig. 5 showsa r-repeaterand associated control relays which are used for -supervisory purposes.

- Fig. 6 shows the arrangement of drawings forming 'part this specification. I

Fig.7shows the arrangement of offices in the trunking system.

The apparatus disclosed in the foregoing drawings is of a type well known in the art and does not require explanation.

Let it be assumed that -a subscriber at station A w ishes 'to bebon-nected with the subscriber at stationJ which connection requires the line to be -extended through a tandem switchboard. The removalof the receiver at station A operateszline relay 103 to'light lamp v104. The subscribefls switchboard operator thereupon inserts plug 120 ofcord circuit 110 intotheline ack 101. A circuitis thus established for cutofi relay 102 from ground, through-its win'ding, sleeve-of,j ack 101, sleeve of Epl-ug 1-20,resistance 116 to battery through lamp 112 and through resistance 1'17 and the contact of relay 113. Relay 113 operates when plug 120isinserted in j ack 101 over the subscribers loop,there-fore, lamp 112 is not lighted vat this time since the current flow through its filament is shunted by resistance 117. The :subscribers switchboard operator requests -.the stationcall-from subscriber A and I upon :findingthata tandem connection is required inserts plug 121 into jack 126. A circuit is thus established for lighting lamp 115 andoperatingrelay 132. i The circuit for lamp 115 is obvious and need not be traced. The circuit for relay 132 extends from ground, through its low resistance and high resistance windings, lower 'winding of coil 128,ring-of jack'126 and plug 121, winding of relay 114,-winding- D of'repeating coil 111 to battery. Relay 1141s not operated in the circuit traced and therefore lamp 115 remains lighted. The :operation o'f relay 132 establishes a bridgaacro'ss trunk 200-which extends .to the tandem loperators :position circuit. This bridge furnishes :an operating circuit for relay 204 which may 'be traced from ground, through :normal contact :2 of relay 206, upper winding of relay 204,normal contact lof relay-202, tip conductor of trunk 200, contact of relay 132, winding of polarized relay 131, ringconductonof trunk 200, normal contact-4 of'relay v1202, lower windingof relay 204 :to battery through normal contact 3 of-relay1206. Polarized relay 131 does not operate in the-circuit traced since the current flow is in=the :wron-grdireetion" for its operation. The operation .of relay 204 establishesa-tircuit for operating relay 214 from ground, through the normal contact 2 of rea plurality of switches for lay 218,

normal contact 2 of relay 210, normal contact 3 of relay 202, contact of relay 204, winding of relay 214 to battery. The operation of relay 204 also establishes a circuit for lighting lamp 216 which may be traced from battery through the lamp filament, resistance 212, normal contact 4 of relay 206, normal contact 3 of relay 207, contact of relay 204, normal contact 3 of relay 202, normal contact 2 of relay 210 to ground through normal Contact 2 of relay 218. The operation of relay 214 establishes a circuit for relay 155 which may be traced from battery, through the winding of relay 155, normal contact 1 of relay 211, contact 2 of relay 214, normal contact 3 of relay 202, normal contact 2 of relay 210 to ground through normal contact 2 of relay 218. The operation of relay 155 establishes an obvious circuit for relay 154. The circuit for relay 154 is, however, estab: lished through a train of, contacts on relays similar to relay 155. A plurality of trunks such as shown in Fig. 2 are used in each trunk switchboard position. Since these trunks are arranged for automatic listening some means such as the chain of relays represented by relays 155 to 157 must be used to prevent more than one trunk circuit being associated with .telephone circuit 136 at the same time.

lNhenever an operator is directing the work at atandem position her headset constituting transmitter 160 and receiver 161 is connected through jacks with the telephone set 136. A circuit for operating relay 137 is thus .established through transmitter 160 to ground through the left windings of induction-coil 162 and the operation of relay 137 establishes an obvious circuit for operating relay 152. The operation of relay 154 thus establishes a circuit for operating relay 147 which may be traced from ground, through the winding of relay 147, resistance 150, normal contact .of relay 149, right winding and contact of relay 151, contact 2 of relay 152, contact 4 of relay 154, resistance 213 and left winding of relay 211 in multiple to battery, through contact 1 of relay 214.

At this point in the operation three short impulses of tone are transmitted to the subscribers operator as a signal that the telephone set of the tandem trunk operator is associated with trunk 200 and that the office designation may be transmitted to the tandem operator. The operation of relay 147 establishes an obvious operating path for relay 144 which looks to ground through its contact 5 andthe normal. contact of relay 145. The operation of relay 144 connects winding 142 of the tone transformer through contacts 3 and 4 of relay 144 and normal contacts 1 and 2 of relay 148 to the conductors oftrunk 200. Acircuit is established at'the same time through the primary winding 141 of the tone transformer which may be traced from battery, through the constantly rotating interrupter 140, winding 141,'normal contact 2 of relay 138 to ground through contact 1 of relay 144. The tone generated in this circuit is transmitted by induction into winding 142 and thence to the subscrib'ers operator. A circuit is also established from ground, through contact 2 of relay 144 for operating relay 138. The latter relay is slow to operate which permits an impulse of tone to be transmitted over the trunk before its operation. The operation of relay 138 opens the circuit through the primary winding of the tone transformer for terminating the first impulse of tone which is known'as a zip tone. A circuit is also established for operating relay 139 from battery, through its winding, contact 1 of relay 138 to ground through contact 2 of relay 144. Relay 139 is slow to operate in order to leave the properopen period between the periods that tone is associated with the trunk. Relay 139 again establishes a circuit through the primary Wind ing of the tone transformer which may be traced from ground, through contact 2 of relay 139, normal contact 1 of'relay 143,.winding 141 to battery through interrupter 140. An obvious circuit is also established for the operation of relay 143 which is slow to operate 'for permitting the transmisison of the second zip tone. The operation of relay 143 opens the circuit through the primary Winding 141 and establishes an obvious circuit for operating relay 146. This relay is also slow to operate for permitting an open period between the second and third zip tones. The operation of relay 146 again establishesthe circuit through the primary winding 141 of the tone transformer and also establishes an operating circuit for slow operating relay 145. The third zip tone is transmitted before the operation of relay 145 which opens the holding circuit for relay 144 to disconnect the secondary winding of the tone transformer from the trunk. The operation of relay 145 also establishes an-obvious operating circuit for relay 148 which associates the tandem operators telephone circuit 136 with the subscribers operators telephone circuit connected to cord circuit 110. Relay 148 looks through its contact 4 to ground at contact 5 of relay 154. The subscribers operator thereupon furnishes the tandem operator with the office name to which the tandem 1 trunk must be connected. The tandem operator immediately inserts plug-222 into the jack of a trunk which is extended by trunk conductors to the proper completing-trunk ofiice. As soon as the tandem operator has received the ofiice name the emergency key 153 may be operated for immediately disassociating the telephone set from the trunk. A circuit is thus established through contact 3 of relay 152 for operating relay 149.- The operation of relay 149 establishes an obvious circuit through the left winding of relay 151 to cause the operation of relay 151 for releasing relay 147 and disconnecting the trunk circuit-from'the common telephone apparatus. Relay 145 is held in an operated position until the train of relays 138, 139, 143 and 146 release. These relays are slow releasing as well as slow operating and suflicient time elapses for the transmission'of the oflice name before the release of relays 145 and 148. If key 153 is not. operated the release of relay 148 awaits the operation of other apparatus here-f inafter described. v x i Upon theinsertion of plug 222 in the jack 300 relay 215 or relays 217 and 215, operate dependingupon whether jack 300 is connected to a long trunk requiring a repeater or a short trunk which does not require a repeater. Let

it be assumed that the trunk associated with V The sleeve of jack jack 300is of sufficient length to require the insertion of the repeater. 300 is connected tot-he high. resistance 302 for discriminating purposes in order to prevent the operation of relay 217 and cause the operation of relay 215. An obvious circuit for operating relay 209 is'established through contact 1 of relay 215. The operation of relay 209 operates relay 211 for opening the operating circuit for relay 155. The circuit for relay 211-may -be traced from battery,. through contact 3 of relay 209, right winding of relay 211 to ground through normal contact 1 of relay 207. The release of relay; 1% releases relays 154 and 148.

The release of relay 148 disconnects thetrunk from the common telephone apparatus. Contact 2 of relay 209 does not'establish' anyfcircuit'at;

this time. Relay215 in addition to establishing a circuit'for relay209 establishes a circuit for operating relay 218 which may be traced fromground' at contact 2 of relay 215,

normal contact of relay 217, normal contact 2 of relay 219 to battery through the Winding of relay 218. The operation ofrelay 218 opens the circuit for lamp216 extinguishing the lamp and alsoopens the operating circuit for relay 214. to cause its release. A circuit is also established-by the operation of relay 218 for marking a terminal on switch 410 which may be traced from battery,

through the winding of relay 219 in multiple with resistance 220,. contact 40f relay 218 to a terminal associatedwith brush 413. The terminal on switch 410 representing the tan-1' dem trunk is thus designated for connection 0a repeater. Conductors 230 and 231 are connectedtogether at contact 1 of relay 218 for starting the operation of'the link circuit,

Fig. 4. Relay448 is operated in this circuit which circuit may be traced from battery, through theleft winding of relay 448, normal contact3 of relay 440, conductor 231, contact 1 of relay 218 toground connectedto conductor 230. o The relays 440, 441 and 442 are representative-of a chain. of relays for distributing the trunk connections to idle links. 1

7 The operation of relay 448 establishes an energizing path for :relay 418 which ;may be traced from battery, through thewinding of the. latter relay, normal contact of switch magnet 419, normal contact 2 of'relay 447, contact 3 of relay 448, normal contact 3 of'relay445 to groundconnected to conductor 230. The energization of relay 4'18 establishes an operating circuit forswitch stepping magnet 419 over the .operatingjpath forrelay 418 excluding the contact of magnet .419. \Vhen the stepping magnet 419 attracts its armature the circuit for relay 418 is opened which causes its release. The release of relay 418 causes the release of magnet 419 advancing the brush assembly of switch 410 one position.

* The operation and release ofrelay 41.8 and stepping 'magnet 419 continue until the markedterminal is associated with brush 413. It. will be noted that the first terminal of switch 410 is connected to the trunk conductors. Thus brush413 is associated with battery extending from relay 219 as previously traced when it has taken one step. The association of battery with brush 413 establishes a circuit for operating relay 447 V which may be traced from the battery on the terminal associated with brush 413, through the normal contact 1 of relay 440, low resistance winding and high resistanceqwinding of relay v447, contact 3 of relay 448, normal contact 3 of relay 445 to ground connected to conductor 230. A locking circuit is established for relay 447 from battery, through its winding M and contact 2, through contact 3 of relay 448, normal contact 3 of relay 445 to ground connected to conductor 230.

. The combination of contacts assembled as contact 2 of relay 447 is such that the ground from conductor 230 is extended through the low resistance-winding of relay 447,.normal contact 1 of relay 440, brush 413 and its associated contact, contact '4 of relay 218 to battery through the winding of relay 219 which causes the operation of the latter relay. Relay 219 locks throughits contact 2 to ground at contact 2 of relay 215. The operation of, relay 219 also opens the operating circuit for relay 218 which causes the release of the latter relay. A circuit is also established at this time for the operation of relay 210 which may be'traced from battery, through contact 1 of relay 219, winding 7 of relay 210 to ground at normal contact 3 of relay 208. Relay 210 does not serve any purposeat this time butla-ter is used for establishing circuits for a switch contact clean ing circuit arrangement.

The operation of relay 447 opens the energizing circuit for relay 418 and magnet 419 and establishes .a circuit for the operation of relay 408. This latter circuit may be traced from ground through contact 1 of relay447, normal contact 1 of relay 444, normal contact of the stepping magnet 409 to battery through the winding of rela 408. The operation of relay 408est-ablishes an operating circuit for magnet 409 which may be traced from battery, through the stepping magnet, contact of relay 408 and thence'to ground at relay 447 as previously traced. The operationof magnet 409 opens the operating circuit for relay 408 causing its release. The release of relay 408 opens the energizing circuit for magnet 409 causing itsrelease which advances the brush assembly of switch 400 one step. It will benoted that ground through contact 1 of relay 447 is connectedto brush 415 which is associated in position .1 with position 1 of brush 405. Therefore, when the switch 400 has taken one step a circuit is established for relay 444. The operation of relay 444 opens the energizing circuit for relay 408 and magnet 409 and switch 400 is brought to rest after it has taken one step.

Simultaneous with the operation of switch 410 a circuit is established for the operation of switch 430. Relay 438 is operated from a circuit extending from battery, throughits winding and the contact of magnet 439 to ground at contact 1 of relay 4.48. The'operation of relay 438 establishes a circuit "for stepping magnet 439 which may be traced from battery, through the winding of the magnet, contact of relay 438 to ground at contact 1 of relay 448 as previously traced. Relay 438 and magnet 439 alternately operate and release to rotate the brush assembly of switch 430 in search of an idle repeater. An idle repeater is characterized by battery connected to the terminal associated with brush 433. It will be noted that this battery is supplied through the winding of relay 500 and normal contact 1 of relay 501. The circuit arrangement shown is such that the switch 430 encounters an idle repeater on the first terminal; At this time the circuit through relay 500 is extended to brush 433, contact 4 of relay 448, normal contact 6 of relay 443, low resistance and high resistance windings of relay 446 to ground at contact 1 of relay 448. Relay 446 operates in the circuit traced and opens at its contact 2 the circuit for relay 438 and stepping magnet 439.

Relay 500 also operates inthe circuit traced which establishes a circuit through its contact 1 for energizing relay 506. This circuit may be traced from battery, through the left winding of relay 506, left winding of coil 505, normal contact 2 of relay 507, winding otcoil514ycontact 1 ofrelay 500, resistance 513, winding D of coil 514,- normal contact f relay 507 right-hand winding of coil 505, right-hand Winding of relay 506 to ground. The operation of relay 5-06 establishes an obvious circuit fortheoperation of relay 509. Relay 509 performs no functionat this time. p H I The operation of relay 446, in addition to the above,establi shes a circuit for energizing relay'428 from battery, through the winding of the latter relay, normal contact of net 429, normal contact 4 of relay 445 to ground through contact I of relay 446.- The 5 operation of relay 428 establishes an energizing circuit for magnet 429 from battery, through the magnet winding, contact of relay 428to ground as previously traced, to contact 1 of relay 446. The operation of the a stepping magnet opens the circuit for relay 428 which releases'and in releasi-ngopens the circuit for the stepping magnet 429. The

release of the steppingvmagnet advances the brush assembly of the switch 420 one step where brush 425 is associated with battery.

through'the winding-of relay 501 and brush 426 is associated with ground through brush 431 and contact 1 of relay 446. The latter connection establishes an operating circuit for relay 445 which opens the energizing cir-' cuit for relay 428 and magnet 429. Relay 443 now operates over a circuit from battery,

through its winding, contact 2 of relay 445 to ground at contact f relay 444. The oper- 7 ation of relay 443 establishes a circuit for the operation of relay 449 which circuit may be traced from battery, through the winding of relay 449, contact 2 of relay 444, contact 1 of relay 445 'to ground through contact 5 of re+ lay 443. r The groundfrom contact 5 of relay 443 is alsoextended through brush 425 to battery through the winding of relay 501 which operates relay 501. c Both ends of an idle repeater have now been selected by switches 420 and 430 which have been connected through the brush menibers and associatedcontacts of switches 400 and 410 to the trunk circuit. A number of circuits are established bythe operation of relay 501 one of which places relay 448 under the control of the repeater circuit. This circuit may be traced from ground, through contact 1 of relay 509, contact 1 of relay 501,

a brush 433 and 'itsassociated contact, contact 1 of relay 449 to battery through relay 448. It will be noted that the operation of relay 449 establishes through its contact 2 an operating circuit for relay 440'. The operation of re lay 440 opens the original energizing circuit through the left winding of relay 448. This relay would therefore have released if a circuit were not established through its right winding; Relay 500 releases upon the operationof relay 501. A circuit for relay 506 extending through contact 1 of relay 500 is thus opened. A second circuit is, however, estab: lished forrelay 506 which extends 'through brushes 423 and 424, contacts Sand 4 of relay 443, brushes "403 and 404 and contact 4 of relay 210 which latter relay was operated upon the operation of relay 219. A circuit for the operationof relays 512 and 524 was also e stablished through the contacts of relay 501 which may be traced from battery, through the windings of relays 512 and 524, normal contact 2 of relay 502, contact 2 of relay 501 to ground through contact 1 of relay 509. The circuit for relay 506 is again changed upon the operation of relay 512 and now exof the latter relay.

The contacts of brushes such as used with step-by-step switches 400, 410, .420- and 430 very often become dirty from oxidation or the accumulation of dust particles which forms an effective resistance thatwould cause an unbalance of theline. In order to elimi- V nate this contactresistance a comparatively high potential is transmitted overa circuit which extends through the brush members and associated contactsthat are connected tends through resistance 513 and contact 4 with the talking conductors. This circuit is 1 its associated contact, contact 2 of relay 512,

brush 435 and its associated contact, contact 4 of relay 449, brush 412 and its associated contact,contact 3 of relay .210, brush-411 and its associated contact, contact 5 of relay 443, brush 436 and its associated contact, contact 4 of relay 524, brush 422 and'its associated contact, contact 2 ofrelay. 443, brush i402 and its associated contact, contact1 of relay 210, brush 401 and its associatedcontact, contact 1- of relay 443, brush 421 and its associated con tact to ringing ground through contact 3 of relay 424. A plurality of relays are operated to control the timing of the application of the high potential for cleaning the brush contacts. Relay 504 is operated frorn'battery, through its winding,normal'contact 1 of relay 502, contact 2 of relay 501 to ground at contact 1 of relay 509. The operation ofrelay 504 establishes an obvious circuit for the operation of relay 503 and the operation of 'relay 503 establishes an obvious operating circuit for relay'502. Relay502establishes a locking circuit for itself through its contact 1 and contact 2 of relay 501 to ground at .contact 1' of relay 509. Relay 502 opens the energizing circuit for relay 504 and the original energizing circuit for'relays 512 and 524.

A second circuit is, however, established for relays 512 and 524 through contact 2 of relay 503 and remains-established until slow release relay 504 releases relay 503. Relay 504 is carefully designed to release within a predetermined time and thus cause the release of relay 503 after the switch contacts have been thoroughly cleaned. VVith relay 502 operated and relay 503 released the energizing circuit for relays 512 and 524 is opened to cause their release which disassociates the ringing current source from the switch brushes.

At this time a circuit is established for relay 530 from battery, through normal contact 2 of relay 500, normal contact 1 of relay 524, winding of relay 530, normal contact 1 of relay 508 to ground through contact 1 of relay 509. Relay 530 is operated at this time to open the repeater for use in connectionv with the completing trunk operators telephone cir cuit, Fig. 3. A circuit is further established at this time for the operation of relay 202, Fig. 2, which circuit may be traced from battery, through contact 1 of relay 219, winding of relay 202, brush 414 and its associated contact, contact 3 of relay 449, brush 434 and its associated contact, contact 3 of relay 502 to ground through normal contact 1 of relay 503. Theoperation of relay 202 establishes a circuit for operating relay 208 which may be traced from battery through contact 1 of relay 219, winding of relay 208 to ground through contact 2 of relay 202. The operation of relay 208 opens the energizing circuit for relay 210 which causes the release of the latter relay. Relay 208 also establishes a locking circuit for itself from ground, through its contact 3 and winding to battery through contact 1 of relay 219'.

A The repeater is now included in the trunk and the extension carried forward through plug 222 and jack 300 to the tandem comple ing trunk switchboard. Apparatus at the latter switchboard is now operated to automatically associate a position operators telephone set with the trunk conductors. A circuit is established for the operation of relay 303 from battery, through its upper winding, normal contact 1 of relay 304, winding C of coil 305, ring of jack 300 and plug 222, contact 2 of relay 209, contact 4 of relay 208, brush 411 and its associated contact, contact 5 of relay 449, brush 436 and its associated contact, normal contact 4 of relay 524, winding F of coil 519, left winding of coil 511, contact 2 of relay 509, winding of relay 510, right winding of coil 511,winding D of coil 519, normal contact 1 of relay 512, brush 435 and its associated contact, contact 4 of relay 449, brush 412 and its associated contact, contact 1 of relay 208, tip of plug 222 and jack 300, winding A of'coil 305, normal contact 2 of relay 304 to ground through the lower Winding of relay 303. The operation of relay 303establishes a circuit for relay 326 from ground, through the contact of relay 303, normal contact'2-ofrelay, 325-, left wind? ingof relay 326 to battery. The operation of relay 326 establishes an operating; circuit for relay 325 and aholding circuit for" relay 326 which may be traced from battery, through the right windings of relay 325 and 326, contact 2 of relay 326', normal contact 2 and lower winding of relay 308 to ground through the contact of relay 303. Relay 308 does not operate in the circuit'traced': Relay 325 in operating establishes a locking circuit for itself from battery, through its-left winding and contact 2 to ground through the contact of relay303. The circuitthrough theleft, winding of relay 326 is opened by the operation of relay 325. A circuit is now established for lighting lamp 314 which may" be traced from. battery, through the lamp filament, contacts. 1 of relays 3'25'and 326' toground through resistance 327 A circuit is also established" at this time for relay 316' through contact 3' of. relay 3262 The operation of relay 3162 establishes" anobvious circuit for relay 317i Relays- 316 and 317 are in a train of relays arranged" topermit the association of only one call at a time with the common apparatus of" the trunk circuit including the operators telephone head set.

Whenever the operator is at the switch board position, transmitter 341 and receiver 342 are associated with the-telephone set 324. A circuit is thus established forrel'ay 339 which is used in place of the retardation coil ordinarily a part of the telephonecircuit. The operation of'relay 339 establishes an ob vious circuit for the operation of" relay 318. Thus relays 339' and 31 8 are normally operated when the telephone operator is at the switchboard position. The operation ofrelays 316 and 317 therefore closes a circuit for relay- 329 which may be traced from ground, through the normal: contact 4 of re lay 330, winding ofrelay 329; contact 3 of relay 318, contact 2 ofrel'ay 317, contact 20f relay 316, to battery through the right win-ding of relay 325. Relay 329 establishes a locking circuit for itself through its contact 2. A circuit is also established for the operation of relay 328 from battery, through. its winding, contact 4 of relay 318,. contact 4 of relay 317, windingof" relay 306, to battery through windingD of coiL 305. Relay 328 operates in the circuit traced but since. its winding is of high resistancethe supervisory relay 306 does not operate.v The circuit path through the winding of relay 306 is merely used for the sake of convenience and economy. The operation of relay 328 establishes a circuit for relay 320,. which maybe traced from battery,.through the winding of relay 320, normal contact'2i of relay 330', contact of relay 328, to ground through the normal contact of relay Relay 320. inoperating establishes a locking circuit for iti the subscribers operator.

. self from ground through its contact 4 under the control of relay 330 or relay 328. I Relay 320 in operating connects the secondary winding 32101 the tone coil with windings D and B of repeating coil 305 and also establishes a circuit for the primary winding 322 of the tone coil for transmitting an impulse of tone by induction through Winding 321. V This tone is also transmitted by induction to windings A and'C of repeating coil 305 and thus transmitted to the subscribers operator through cord circuit 110.

I The circuit for the secondary winding 321 is obvious and need not be traced. The circuit for the primary winding extends troin flashing the lamp 314 during the transmission of tone to the subscribers operator. Relay 336 is first operated over a circuit traced from battery, through its winding, contact 5 of relay 320, contact 5 ofrelay 317 contacts 1 of relays 325 and 326, to ground through resistance 327. Relays 338 and 337 operate in response to the operation of relay 336. The relays 337 and 338 are slow to operate in order that sufficient time may be permitted to elapse between flashes ofthe lamp. Upon the operation of relay 337, battery is connected through its contact, over a circuit extending through contact 5 of relay 320, contact 5 of relay 317, to ground through contacts f relays 325 and 326 and resistance 327. This battery circuit efi ectively shunts the current flow through the filament of lamp 314 which extinguishes the light. The battery at the contact of relay 337 also shunts the current from relay 336 causing its release. Following the release of relay 336 both relays 338 and 337 .release which permits relay 336 to again operate. This procedure continues until the flashing circuit is opened. r i

When the circuits are established for the primary and secondary windings 321 and 322 of the tone coil a circuit is also estab lished for the operation of relay 335 front ground, through'contact 1 of relay 320, normal contact 2 of relay319, to battery through the winding of relay 335.- This relay is slow to operate in order to permit thetransmission of an impulse of tone of short durationto Two impulses of tone are transmitted to the subscribers operator to advise her that the telephone set 324 at the completing trunk operators position is associated with the trunk. The operation of relay 335 opens the circuit through the primary winding 322 of the tone coil to terminate the transmission of tone and establishes an obvious circuit for the operation of relay 334. The latter relay is slow to operate,

thus permitting 1 an interval between'f'the transmission of tone imp'ulses. .1 When relay 334 operates, the circuit for the primary winding 322 of the tone coil is again establishedthrough contact/f relay 335 and con-' tact 2015 relay 334 to ground through contact 2 of-relay332. The operation ofrelay 334 also establishes an obvious-circuit for .the e I operation of lrelay"332..%YThe' latterlrelay is slow to operate in orderto permit the trans mission of a tone impulseILWh'en this relay operates the circuit through the primary winding 322 of the tone coil is permanently opened and the tone induction circuit through condenser 333 is also opened: The operation of relay 332 further establishes an obviou circuit'foroperating relay 319. 3 r

The'operation of relay- 319 connectsthe I operatorstelephonehead set'with the trunk circuit in order that the called-station desig nationmay be transmitted to the completing trunk operator by the subscribers operator.

This designation'is transmitted by the-s ub: scribers'operator immediately upon the re:

ceptionof the second impulse oftone. Phe operation of relay 319- further establishesj a locking circuit for relay 332 from battery,

through the winding of the latter relay, contact 2 of. relay 319, to ground through con tact 1 of relay 320. A circuit is also. established from battery through contact 3- ofrelay 319 for operating relay: 330 extending through the winding of'relay 330, to ground at contact 1 of relay 329. Relay 330 in operating establishes a locking circuit forjitself to ground through itscontact' 3. It willgbe noted that the circuit for relay 335 is opened atcontact 2 of relay 319'-an d therelea se of relay 335 causesv the release ofrelay 334. .5 The operation ofrelay330, establishesv anobvious circuit for operating relay 331. to remove-the control of relay 320 from relay'331- A circuit 7 is, however,'established for holdingrelay 320 through contact 2 of'relayr330 to ground through contact 1 ofrelay-. 3 29. 7

The completing trunk operator now. tests the line leadi g to the desired subscribers station by touching the tipfof plug 315 tothe sleeve of jack 340 in the well knownmanner of testing lines. If the lineisidle plug 315 bered that a circuit was. previously. .established through the lower winding ofrelay, 308

which assists in the operation of the relay. The circuit through the lower. winding, is, however, opened. as the relay completes. its operation, and the relay is held operated through its upper winding.- The operation of relay 308 opens at its contact 2 the circuit for-relay 326 which latterl rgleasycevsf Tharelays released in. consequence, of: the release: of relay; 325 are as: follows:- The cir= suit for relay 316 is opened at the contact. 3 :5 relay'326; The: release: of relay 316- opens thezcircuiitfor 1'.&lfiy'3l"T;.. The: release of'relay 3'17. opensthe circuit for" relays 336, 337 and 338 and: also: opensithecircuits-for relays 328 and 329. The; release of relay 329 opens the circuit for relay 320.. The release; of? relay 320,; opens the circuit for relay= 332: and: the relhase of relay'332 (ilDfiIISil'ihB? circuit for relay 319;. Therelease' oii relay 3L9) opens the cir= cuit' for" relay 330. which, turn. opens the circuit for relay" 331..

operation or relay: 308: establishes circuits tor connecting ringing current to the subscribers station for sounding the bell at that-station; Relay'307 is operated for this purpose: from battery. through its winding, normal. contact cit relay 311', normal. contact of relay- 312,.contact 2: of relay: 308, normal contactzr of? relay 326, contact 1 of relay 325, IIPID'GU'WlHdhHQOfIGlEY 308.to ground through the winding ofi-relay 343. Ringing current is: extended overthezline from ringing source 31:3 throughtheawinding'of relay 31-2, contact 22. of relay 30 7",. thence over the line and through the ringer windings at subscribers station. J returninggto: ground through contact B of rel'ay 307". A. ringing'induction tone is transmitted to; the' calling: subscriber at station A throughcondensers 309 and 310. the subscriber at station J removes-the receiver from the switchhook, sufiici'ent energy 'is carried through the winding of relay 312 tocause its operation. The operation of relay 312 opens the short circuitaround the \vinding of relay 311 which permits the op eration ofrelay 31 1 in serieswith relay 307.

= Uponthe: operation of relay 31 1 battery is connected to its armature which shunts the currentfrorrrthe-winding of relay 307'- to cause itsreleaseand disconnect the ringing current fromthe-subscriberslihe. Relay 311 also establishes a locking'circuit for'itself tomaintai'rr relay released.

Upon the releaseof relay 307 after the removal ofthe receiver from the switchhook a circuit, is established for relay- 306 over the su'hscribers line and through the-station apparatus which circuit'is'obvious and need not be traced; The operation of'relay 306 establishes an obvious circuit for operating relay 304, for reversingthe direction ot current flow over the trunk conductors. The circuit over which the current fl'o-w is-reversed is the same as traced; for the operation of relay 303 except that as a result of this reversal, battery i'srextended over the tip conductor and ground over the ring conductor through the winding of polarized relay 510, Fig. 5'. The current flow is now' in the proper direction to cause the operation ofrelay' 510. A circuit is thus established to operate relay 508. which looks the. operation of relay 508. ground is ex;- tended from the contact of relay 510 through contact 1 of relay 503,v winding of relay 530, normal contact 1 of relay 524, to battery through the-normal contact 2 of relay 500. The operation and release 0t relay 530 is now placed under the control of the subscriber at station A. Relay 530 is operated and released in the manner shown to prevent disturbances in the repeater circuit. The operation of relay 510'also controls the operation of relay 507 for reversing the current flow over the trunk extending tothe subscribers switchboard, in order to operate the polarized relay 131. With relay 507 operated the circuit for relay 131 may be traced from battery through the left winding of relay 506, left winding of coil 505, contact 2 of relay 507, winding D of coil 514, normal contact 2 of relay 512, brush 424 and its associated contact, contact 4 of relay 443, brush 404 and its associated contact, contact 1 of relay 202, contact of relay 132, Winding,- of relay 131,. contact 4 of relay 202, brush 403 and its associated contact, contact 3 ofrelay 443, brush 423 and its associated contact, normal contact 3 of relay 512, winding, B of coil 514, contact 1 of relay 507 right winding of coil 505, right windingoit' relay 506 to ground. The operation: of polarized" relay 131: establishes a loop circuit for the operation of supervisory relay 114, through the low resistance winding of relay 132. This circuit may: be traced from battery through Winding: D of coil 111, winding of relay 114, ring of plug 121 and jack 126, lower winding of coil 128, upper low resistance winding of relay 132', contact of relay 131, upper winding of coil 128, tip of jack 126 and plug 121, to ground through winding B of coil 111. The operation of relay 114 establishes a shunt for-lamp 115 by associating battery through resistances 118', 119 and 127, to ground. Lamp 115 is thus extinguished. If the subscriber at station J flashes the switchhook by moving it up and down, it will be seen that relay 306 will be intermittently released and operated, in turn releasing and operating relay 304. The intermittent release and operation of relay 304 intermittently reversesthe current in the winding of polarized relay 510 causing the latter relay to release and operate intermittently. The intermittent release and operation of relay 510 controls the release and operation of relays 507'and 530. The intermittent release and operation of relay 507 reverses the current how in trunk 200 causing the intermittent release and operation of relay 131 for intermittently releasing and op erating relay 114 to flash the lamp at the subscribers switchboard. The operator at the subscribers switchboard is thus signaled that the J subscriber requires attention and associates her telephone set with trunk 200 to ground at contact 1 of relay- 509; Upon through the cord circuit 110. l

:40 the normal contact 1 of relay 207. The opertransmitted to the subscribers operator and alsothat thetrunk operators telephone set 136 has been associated with thetrun-k circuit, Fig. 2, for the transmission of the oflice name. It will be remembered'that for such operation the relays 204 and 214 were operated. Upon receipt of the ofl'ice name plug 222 is associated with a circuit, Fig. 3,as

previously described. Assuming that plug I 222 is insertedinto the trunk jack 300associated with a trunk not of suflicient length to require a repeater, the sleeve of the jack 300 will have connected therewith a low resistance 301. A circuit is thus established to operate both the marginal relay 217 and relay 215. The operation of relay 217 opens the circuit extending between contact 2 of relay 215 and the winding of relay 218 which prevents the operation of relay 218 and thus prevents the selection of a repeater. The operation of relay 215 establishes an obvious circuit'for the operation of relay 209. The operation of relay 209 establishes a circuit for the operation of relay 206 which maybe traced from battery, through contact 3 of relay 209, normal contactg3 of relay 218, normal contact 3 of relay 219, normal contact 2 of relay-208, winding of relay 206, to ground through normal contact 1 of relay 207. Re-

lay 211 also operates from. a circuit estab V lished through its left winding which may be traced from battery at contact 3 of relay 209,1eft Winding of relay 211, to ground at ation of relay 211 disconnects the telephone circuit from the trunk circuit as previously described. The operation of relay 206 dis connects battery and ground from-relay 204 and extends the tip conductor of trunk 200 to the tip of plug 222 and jack 300 of the trunk circuit, Fig. 3. The tip conductor when thus connected reestablishes an operatingfcin I cuit for relay 204 which may be traced from its upper winding, through contact 2 of relay 206, tip of plug 222 and j ack 3O0, winding A lower Winding of relay 204 is extended through contact 3 of relay 206, normal con tact 4 of relay 207, normal contact 4 of relay 208, contact 2 of relay 209, ring of plug 222' and jack 300, winding-C of repeating coil 205, normal contact 1 of relay 304,.upper winding of relay 303 to battery. The relay 204 is thus maintained operated which maintains an energizing circuit for relay 214 tov prevent the operation of relay 207. The calling subscribers station A is thus connected to thehcalled subscribers. station J without I theinsertionof a repeate'r'. .1 Upon the' removal of plug 121, from jack 126, ,relays'204 and-214 are released which permits relay 207 to operate. The circuit for contact 3 of relay 209, winding of relay 207,

normal contact 2 of relay'214, normal contact 3 of relay 202, normal contact 2 of relay 210,

.to ground through normal contact 2 of relay 218, The operation of relay 207 establishesa circuit for lighting lamp 216 from battery through its filament, resistance 212,

to ground ithroughtvcontact 2' of relay 207." This, is a signal for the. trunk operator to oflices, aplurality of trunks of difi'erent char- 'act'eristics outgoing fronian otfice, incoming trunks to said oflice terminating in conductor terminals, means at said oilice forephysically connecting, said conductor terminals with *said outgoing trunks, repeaters common to said trunks, and means operably responsive solely to the se zureof an outgo ng trunk of a certa n characteristic toadd a repeaterfin series with the talking. conductors terminating in said conductor. terminals. V 1 v 2. In a, trunking systemQa plurality of Offices, piura lity oftrunks-of difierent char-v acteristics outgoingiirom'an oflice, incoming trunks to said ofiice terminat ng in conductor connecting v said conduct-or terminals with operable in response to 'sai'dconnection solely for determining th'e character of said out; I going trunk, repeaters common ,to sald trunks,

and means operably responsive to a parti'cue lar operation of said jdiscriminating means for adding a repeater in series with the talk: ing; conductors of saidptrunks,

ln-a trunking system in which a telephoneconnectionis built up by adding successiverlinks, repeaters common to a l nk in said connection, and means controlled solely by a condition individual to one ofsaid links to connect af-repeater to the preceding link t' h d't' of repeatlng 0011 305, contact 2 ofrelay 304, lespon-blve O t 8 ad 1 Ion lower winding of relay 303 to: ground. The

of said one link to said preceding link. f-

cessive links, operators"telephone sets at each link, means responsive to the additionof a I linkto automatically associatean operators telephone set withftlieadded link for instruction sregardingflthejextensionof said link,

repeaters common to a link in said connection, andmeans controlled bya condition individualtoone Ofsaid linksto connect a repeater to a preceding'link responsive to the.

relay 207 may be traced from battery, through 50 v Q. V 1 terminals means at said oi'lice ior h sicall addition of said one link to said preceding lin '5. In a trunking system in which a telephone connection is built up by adding successive links, a plurality of groups of repeaters, each group being common to a plurality of certain links and selectable thereby, and means controlled solely by a condition individual to certain ones of said links to connect a repeater to the preceding link responsive to the addition of successive links.

6. In a trunking system, a plurality of trunks interconnecting two distant points, a plurality of other trunks of various characacteristics interconnecting one of said points with another distant point, means for connecting together the ends of said trunks terminating at said common point, a group of selectable repeaters common to said trunks, and means in a said first trunk automatically responsive to a said connection for selecting an idle repeater from said group and adding it in series with the conductors of said first trunk only if the second trunk is of a character that requires the addition of a repeater.

7. In a trunking system, a plurality of trunks interconnecting two distant points, a plurality of other trunks of various characteristics interconnecting one of said points with another distant point, means for connecting together the ends of said trunks terminating at said common point, a group of selectable repeaters common to said trunks, and means in a said first trunk responsive to a said connection for determining the character of the second trunk for add-V ing a repeater in series with the conductors of said first trunk or for preventing suchaddition.

'8. In a trunking system, a plurality of trunks interconnecting a first point and a distant point, a second plurality of trunks of various characteristics interconnecting said distantpoint and a second distant point, a line, means to connect said line with the trunk at said first point, operators telephone sets at each point, means automatically operable in response line to the trunk at said first point for connecting the operators telephone set at said distant point to said same trunk, means for connecting the end of said same trunk to the end of a trunk outgoing from said distant point, repeaters, and means in said same trunk automatically responsive to said latter connection for distinguishing the character of the trunk connected therewith and for adding a repeater in series with the conductors ofsaidtrunk if the character of the trunk requires such addition.

'9. In a trunking system, a plurality of trunks of difierent characteristics extending from one oifice to a distant oifice, -a plurality of other trunks incoming from various points automatically to the connection of said 7 and terminating at said first ofice, means for connecting the terminating end of said other trunks directly with the outgoing end of said trunks of diiierent characteristics, repeaters, means operable responsive to said connection solely for distinguishing an outgoing trunk of a character that requires the addition of a repeater, and means responsive to the operation of said distinguishing means for connecting a. repeater in series with the conductors of the trunks.

10. In a trunking system, a plurality of trunks of difierent characteristics extending from one oifice to a distant ofiice, a-plurality of other trunks incoming from various points and terminating at said oilice, means for connecting the terminating end of said other trunks directly with the outgoing end ot said trunks of different characteristics, repeaters, means operable responsive to said connection solely for distinguishing outgoing trunks that require the addition of a repeater and those that do not require such addition, and means responsive to a certain operation of said distinguishing means for connecting a repeater in series with the conductors of said trunk.

11. In a trunking system, a plurality of trunks of difierent characteristics extending from one oflice to a distant office, a plurality of other trunks incoming from various points and terminating at said first ofiice, means for connecting the terminating end of said other trunks directly with the outgoing end of said trunks of difierent characteristics, repeaters, and means operable responsive to said connection solely for distinguishing the charac ter of an outgoing trunk for either causing the selection of an idle repeater for said trunk or for preventing the selection of a repeater.

12. In a trunking system, a plurality of trunks of different characteristics extending from one ofiice to a distant office, a plurality of other trunks incoming from various points and terminating at said first ofiice, means for connecting the terminating end of said other trunks directly with the outgoing end of said trunks of different characteristics, a common group of repeaters for said other trunks, and means operable responsive to a said connectionsolely for distinguishing the character of a connected trunk for causing the selection ofan idle repeater in said group and for connecting the selected repeater in series with the conductors of said trunk.

13. Ina trunking system, a plurality of trunks of difierent characteristics extending from one ofiice to a distant office, a plurality of other trunks incoming from various points and terminating at said first office, means for connecting the terminating end of said other trunks directly with the outgoing end of said trunks of different characteristics, acommon group of repeaters for said other trunks, and means operable responsive to a said connection for solely distinguishing the character of a connected trunk for either causing the selection of an idle repeater in said group or for preventing said selection.

14. In a trunking system, a first switchboard, a second switchboard, a third switchboard, trunks extending from said first switchboard to said second switchboard, trunks of' various characteristics extending from said second switchboard to said third switchboard, means at said second switchboard for connecting together the incoming and outgoing ends of any of said trunks, repeaters, and means responsive to a said connection solely for distinguishing the character of the outgoing trunk and for adding a repeater in series with the conductors of said trunkwhen the character ofsaid trunk is such as to require a repeater.

15. In a trunking system, a first switchboard, a second switchboard, a third switchboard, trunks extending from said first switchboard to said second switchboard, trunks of various characteristics extending from said second switchboard to said third switchboard, an operators telephone set at each switchboard, means at said second switchboard responsive to a connection to a trunk at said first switchboard for connecting the telephone set at said second switch board with said trunk, means at said second switchboard for physically connecting the in coming end of the trunk to which the telephone set is connected to the outgoing end of a trunk extending to said third switchboard, repeaters, -means responsive to said connectionfor distinguishing the character of said trunk and for connecting a repeater in series with the conductors of said trunk if the character ofthe trunkis such as to require a repeater, and means at said third switchboard operable in response to said connection for connecting the telephone set at said third switchboard "with the trunk extending thereto.

16. In a trunking system, a plurality of trunks of different characteristics extending from jacks in one ofiice to distant offices, a plurality of other trunks which terminate at said first office in a single plug for connection with any of said jacks, repeaters, means operable responsive to such connection for distinguishing the trunks that require the addition of a repeater, and means responsive to the operation of said distinguishing means for connecting a repeater in series with the conductors of said trunks.

17.In a trunking system, a plurality of trunks of different characteristics extending from jacks in one office todistant oifices, a plurality of other trunks, each terminating at said first ofice in a single plug for connection with any of said'jacks, a common group of repeaters for said other trunks, and means operable responsive to a'said connection 'for distinguishingthe character of the trunk so j v connected for causing the selection of an idle repeater in said group, and for connecting said repeaterin series with the conductors of said trunk. I

'18. In a trunking system, a plurality of trunks of different characteristics extending from the jacks in one oflice to distant ofiices, a plurality of other trunks, each terminating at said first ofiice in a single plug for connection with any of said jacks, a group of re tending from jacks in the tandem 'switchboard to plugs in the tandem completing switchboard, operators telephone sets in each switchboard, repeaters available for selection for said trunks, means responsive to a connection withone of said jacks at said subscribers switchboard for connecting the telephone set at said tandem switchboard with the trunk connected to said jack, and means operable in response to the insertion of the plug of said trunk into a jack at said tandem switchboard for selecting an idle repeater and for inserting it in series with the conductors of said trunk. v

20. In a trunking system, a plurality of trunks incomingat a tandem office, a plurality of trunks of different characteristics outgoing at said tandem office and incoming from a second tandem 0ffice,'a plurality of trunks of diflerent characteristics outgoing from said second tandem ofiice and incoming at a completing ofiice, repeaters at said tandem offices, and. means responsive to the connection of the incoming and outgoing ends of the trunks'at the tandem oflice s solely for distinguishing the character of the outgoing trunks and for adding, repeaters in series with either or both of said trunks when the characteristic ofthe trunks requires such addition; v i

21. In a trunking system, a plurality of selectable trunks outgoing from one operators position and terminating in a plug at a sec- 0nd operators position, a plurality of other trunks of different characteristics terminating in jacks in said: second operators posie tion and extendingto a distant operators position, operators telephone sets at each posi- I tion, means at said second operators position operably responsive to the selection of a trunk at said first position for connecting the telephone'setat the :second position to the selected trunk, repeaters, means operable in response to the lnsertlon-of the plug of a selected trunkinto one of said acks for distinguishing-the character of the trunk conposition',,op erators" telephone sets at each position, means at said second operators position operably responsive to the selection of a trunk at said first position for connecting the telephone set at the second position to'the selected trunk, repeaters, means operable in response to the insertion of the plug of a selected trunkinto one of said jacks for distinguishing the character of the trunk connected therewith, means operable in response to a certain operation of said distinguishing means for connecting a repeater.

in series With the conductors of said selected trunk, and lneans at said distant operators position operable in response to the connection of said repeater to said trunk for con necting the distant operators telephone set to the trunk connected to said jack.

' 23. In a trunking system, a plurality of trunks of different characteristics extending from jacks in one oiiice to distant oilices, meansto set up a conditionon the sleeve terminals of said jacks indicative of said different characteristics, a plurality of other trunks which terminate at said first otfice in a single plug for connection with any of said jacks, repeaters,'means operable responsive to'said sleeve condition following the insertion of one of said plugs in one of said jacks for distinguishing trunks that require the addition of a repeater, and means responsive to the operation otsaid distinguishing means for connecting a repeater in series with the conductors of said trunks;

24. In a trunking system, a plurality of trunks of difi erent characteristics extending from jacks in one office to distant ofiices,

plug for connection with any of said jacks,

a group of repeaters common to said other trunks, means operable responsive to said sleeve condition-following the insertion of one of said plugs in one of said jacks for distinguis'hing' the character of the trunk so connected forcausi-ng the selection of an idle repeater in said group and for connecting said repeater in series with the conductors of said trunk.

25. In a trunking system, a plurality of trunks of different characteristics, outgoing from an ofiice, trunks incoming to said ofiice, means for connecting said incoming trunks with said outgoing trunks, repeaters common to said trunks and means in said incoming trunks operable responsive to the seizure of the outgoing trunk of a certain characteristic to add a repeater in series with the talking conductors of said trunk.

26. In a trunking system, a plurality of trunks of difi'erent cl'iaracteristics extending from jacks in one oiiice to distant otfices, a plurality of other trunks which terminate at said first oliice in a single plug for connection to any of said jacks, repeaters, means in said plug ended trunks operable responsive to such connection for distinguishing the trunks which require the addition of a repeater and means responsive to the operation of said distinguishing means for connecting the repeaters in series with the conductors of said trunks.

.27. In a trunking-system, a plurality of trunks of different characteristics extending from jacks in one olfice to distant otlices,

means to set up a condition on the sleeve ter-' minals of said jacks indicative of said diiierent characteristics, a plurality of other trunks which terminate at said first office in a single plug for connection with any of said jacks, means in said plug ended trunks operable responsive to said sleeve condition following the insertion of one of said plugs in one of said jacks for distinguishing trunks that require the addition of a repeater, and-means responsive to the operation of said distinguishing means for connecting a repeater in series with the conductors of said trunks.

In witness whereof I hereunto subscribe my name this 30th day'of August, 1928.

FERDINAND S. ENTZ. 

